Metal-insulator transition in Pt-C nanowires grown by focused-ion-beam-induced deposition

Abstract

We present a study of the transport properties of Pt-C nanowires created by focused-ion-beam (FIB)-induced deposition. By means of the measurement of the resistance while the deposit is being performed, we observe a progressive decrease in the nanowire resistivity with thickness, changing from ${10}^{8}\text{ }\ensuremath{\mu}\ensuremath{\Omega}\text{ }\text{cm}$ for thickness $\ensuremath{\sim}20\text{ }\text{nm}$ to a lowest saturated value of $700\text{ }\ensuremath{\mu}\ensuremath{\Omega}\text{ }\text{cm}$ for thickness $g150\text{ }\text{nm}$. Spectroscopy analysis indicates that this dependence on thickness is caused by a gradient in the metal-carbon ratio as the deposit is grown. We have fabricated nanowires in different ranges of resistivity and studied their conduction mechanism as a function of temperature. A metal-insulator transition as a function of the nanowire thickness is observed. The results will be discussed in terms of the Mott-Anderson theory for noncrystalline materials. An exponential decrease in the conductance with the electric field is found for the most resistive samples, a phenomenon understood by the theory of hopping in lightly doped semiconductors under strong electric fields. This work explains the important discrepancies found in the literature for Pt-C nanostructures grown by FIB and opens the possibility to tune the transport properties of this material by an appropriate selection of the growth parameters.